I will be filming with my iphone, I probably wont take anyone with me so Ill just set it on a bench or something. What angle is best? Parallel to me(facing my chest at release) or behind so you can see the flight of the disc? Or a little of both?

Behind ain't as useful as left of the tee toward the center of the tee. 1 top down, 2 to the side, 3 from in front and 4 from behind.

Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.